On the existence of Ca2Bi-crystal and electronic structure of Ca4Bi2O

Reported are the structure refinements and the electronic structure calculations for the ternary compound Ca4Bi2O, up until now erroneously known as the binary Ca2Bi. Ca4Bi2O crystallizes in the body-centered tetragonal space group I4/mmm (no. 139), with cell parameters a = 4.719(2) Å and c = 16.505(9) Å at 120 K, and its structure can be regarded as built of oxygen-centered octahedra of Ca, forming infinite layers via corner sharing, i.e. as an anti-type of the perovskite-related K2NiF4. The bonding in Ca4Bi2O has been further analyzed using electronic structure calculations (LMTO-ASA), which confirm that Ca4Bi2O and related phases, as expected, are closed-shell compounds.